A wireless power transmission technology or a wireless energy transfer technology that wirelessly transfers electric energy from a power source to a desired device already began to be used in an electric motor or a transformer from the 1800s. Since then, a method was tried for transmitting electric energy by radiating electromagnetic waves such as radio waves or laser beams. Electrical toothbrushes or some wireless razors mainly used by general users are actually charged according to the principle of electromagnetic induction. The kinds of wireless energy transmission schemes are as follows.
First, there is an electromagnetic induction scheme using magnetic induction. The magnetic induction scheme, which induces currents from a coil to another coil through a magnetic field, has limitations in that a load power and a relative position and distance between the coils are required to be accurate. Recently, some companies have begun to launch new wireless charge products that can charge portable terminals, personal digital assistants (PDAs), MP3 players, and notebook computers using the electromagnetic induction scheme.
Second, there is a magnetic resonance method which is a non-radiative wireless transmission technology using a near-field effect. The technology is based on an evanescent wave coupling scheme where electromagnetic wave moves from a medium to another medium through a near electromagnetic field when the mediums resonate at the same frequency. A charge station connected to a power source forms the electromagnetic field, and when approaching a portable device, including a receiver that has been designed at the same resonance frequency of MHz band, to inside the electromagnetic field, a kind of energy tunnel is formed between two mediums, thereby charging the portable device within a distance of several m from the charge station. Particularly, such energy is non-radiative and based on a magnetic field, and thus, only when there is a device having a resonance frequency, the energy is transferred to the device, but an unused portion of the energy is spread into the air and reabsorbed into an electromagnetic field. Therefore, unlike electromagnetic wave, the energy does not affect ambient machines and/or human bodies.
Third, there is a long-distance transmission technology using a short-wavelength wireless frequency within an electromagnetic wave range. The long-distance transmission technology uses an electromagnetic radiation scheme using microwave of 5.8 GHz, but is fatal to human bodies. Accordingly, the magnetic induction scheme and the magnetic resonance scheme have lately been put to practical use. A soft magnetic material used in the wireless charge scheme using the magnetic field is a soft ferrite (hereinafter referred to as “magnetic ferrite”).
In general, the ferrite refers to a magnetic material which is strongly magnetized although an external magnetic field is slightly applied to the ferrite, and in which residual magnetization is small. Although saturation magnetization and residual magnetization of the magnetic material are ⅓ and ¼ of those of a metal material and are relatively small compared to the metal material, since electric resistance of the magnetic material is large, an eddy current loss is small and the magnetic is used at high frequency compared to the metal material. That is, the ferrite becomes a kind of magnet when the external magnetic field is applied, but loses a magnetic force and returns in its original condition when the external magnetic field is removed, and is operated by electric waves. The ferrite is indispensable as the magnetic core of a high frequency transformer and is applied to various uses such as a magnetic core of a communication coil for televisions, radios, etc. and an electromagnetic wave absorber and the like.
However, in a case where a conventional ferrite sintered compact has high damage frequency, its strength is vulnerable to an impact. Thus, when the conventional ferrite sintered compact is installed in wireless devices and the like, the high damage frequency are shown, and due to this, a magnetic property is reduced. As a result, it is problematic that as permeability reduces and a loss rate increases, charging efficiency also reduces.
Also, magnetic energy of the magnetic material such as the ferrite sintered compact and the like is changed to electric energy, and thus is used in wireless charging. However, when the magnetic material is adhered to a different kind of substrate while being used in a state of being changed to thermal energy, a delamination phenomenon occurs due to a difference in coefficient of expansion generated caused by the thermal energy.